Branched Proximal Connectors For High Density Neural Interfaces

ABSTRACT

The present disclosure relates to branched proximal connectors for high density neural interfaces and methods of microfabricating the branched proximal connectors. Particularly, aspects of the present disclosure are directed to a branched connector that includes a main body having a base portion of a supporting structure and a plurality of conductive traces formed on the base portion, and a plurality of plugs extending from the main body. Each plug of the plurality of plugs include an end portion of the supporting structure comprised of the one or more layers of dielectric material, and a subset of conductive traces from the plurality of conductive traces. Each trace from the subset of conductive traces terminates at a bond pad exposed on a surface of the end portion of the supporting structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.16/658,596, filed Oct. 21, 2019, which claims the benefit of priority toU.S. Provisional Application No. 62/768,562, filed Nov. 16, 2018, theentire contents of which are incorporated by reference herein for allpurposes.

FIELD

The present disclosure relates to implantable neuromodulation devicesand methods of fabrication, and in particular to branched proximalconnectors for high density neural interfaces and methods ofmicrofabricating the branched proximal connectors.

BACKGROUND

Normal neural activity is an intricate balance of electrical andchemical signals, which can be disrupted by a variety of insults(genetic, chemical or physical trauma) to the nervous system, causingcognitive, motor and sensory impairments. Similar to the way a cardiacpacemaker or defibrillator corrects heartbeat abnormalities,neuromodulation therapies help to reestablish normal neural balance. Inparticular instances, neuromodulation therapies utilize medical devicetechnologies to enhance or suppress activity of the nervous system forthe treatment of disease. These technologies include implantable as wellas non-implantable neuromodulation devices and systems that deliverelectrical, chemical or other agents to reversibly modify brain andnerve cell activity. The most common neuromodulation therapy is spinalcord stimulation to treat chronic neuropathic pain. In addition tochronic pain relief, some examples of neuromodulation therapies includedeep brain stimulation for essential tremor, Parkinson's disease,dystonia, epilepsy and psychiatric disorders such as depression,obsessive compulsive disorder and Tourette syndrome; sacral nervestimulation for pelvic disorders and incontinence; vagus nervestimulation for rheumatoid arthritis; gastric and colonic stimulationfor gastrointestinal disorders such as dysmotility or obesity; vagusnerve stimulation for epilepsy, obesity or depression; carotid arterystimulation for hypertension, and spinal cord stimulation for ischemicdisorders such as angina and peripheral vascular disease.

Neuromodulation devices and systems tend to have a similar form factor,derived from their predecessors, e.g. the pacemaker or defibrillator.Such neuromodulation devices and systems typically consist of an implantcomprising a neurostimulator having electronics connected to a leadassembly that delivers electrical pulses to electrodes interfaced withnerves or nerve bundles via an electrode assembly. The lead assembly istypically formed of a conductive material and takes the form of aninsulated wire (e.g., a dedicated channel) connected to the electrodesvia a first connector on one end (e.g., a distal end) and theelectronics of the neurostimulator via a second connector on another end(e.g., a proximal end). In some instances (e.g., deep implants), thelead assembly comprises additional conductors and connectors such asextension wires or a cable connected via connectors between theelectrodes and the electronics of the neurostimulator.

Conventional neuromodulation devices include between four and sixteenelectrodes, and thus typically include four to sixteen channels or wiresconnected respectively to the electrodes at the distal end and theelectronics of the neurostimulator at the proximal end. However, thereis a need for high density neural interfaces that include greater thansixteen electrodes to interface with larger tissue volumes, to recruitsmaller populations of neurons for recording, or to provide moretargeted therapy by tailoring the electrical stimulation parameters andactivated tissue volume. Increasing the density or number of electrodescan increase the number of channels or wires needed to connect theelectrodes and the electronics of the neurostimulator. In order toimplement high channel or wire counts, there is a need for reliableelectrical connections that can maintain contact and electricalisolation in a subject body (e.g., a patient body) for many years.Typically, a lead assembly containing a high channel or wire count needsto be permanently connected to the electronics. However, this is notideal because the electronics need to be replaced every few years toupgrade them or to replace batteries, and surgeons have a strongpreference not to remove the lead assembly from the neural tissue due tothe risk to the patient. Therefore, there is a need for reliable andnon-permanent connectors for lead assemblies having high density neuralinterfaces.

BRIEF SUMMARY

In various embodiments, a branched connector is provided that comprises:a main body comprising a base portion of a supporting structure and aplurality of conductive traces formed on the base portion, where thebase portion of the supporting structure is comprised of one or morelayers of dielectric material; and a plurality of plugs extending fromthe main body. Each plug of the plurality of plugs comprises: an endportion of the supporting structure comprised of the one or more layersof dielectric material; and a subset of conductive traces from theplurality of conductive traces, where each trace from the subset ofconductive traces terminates at a bond pad exposed on a surface of theend portion of the supporting structure.

In some embodiments, the dielectric material is polyimide, liquidcrystal polymer, parylene, polyether ether ketone, or a combinationthereof. In some embodiments, the plurality of conductive traces arecomprised of one or more layers of conductive material, and theconductive material is platinum (Pt), platinum/iridium (Pt/Ir), titanium(Ti), gold/titanium (Au/Ti), or any alloy thereof.

In some embodiments, a coefficient of thermal expansion for theplurality of conductive traces is approximately equal to a coefficientof thermal expansion for the supporting structure.

In some embodiments, the base portion of the supporting structure andeach of the end portions of the supporting structure are monolithic.Optionally, each of the end portions of the supporting structure areplanar. Optionally, each of the end portions of the supporting structureare a cylindrical tube.

In some embodiments, the one or more layers of dielectric materialcomprise a first layer of dielectric material and a second layer ofdielectric material with the subset of conductive traces buried betweenthe first layer of dielectric material and the second layer ofdielectric material.

In some embodiments, each bond pad is a split annular ring positionedaround an axis of the cylindrical tube and exposed on the surface of thecylindrical tube. Optionally, each split annular ring is spaced apartfrom one another on the surface of the cylindrical tube by a region ofthe first layer of the dielectric material. Optionally, a width of theregion of the first layer of the dielectric material that separates eachsplit annular ring is between 1.0 mm to 10 mm.

In some embodiments, the cylindrical tube comprises: (i) the one or morelayers of dielectric material, wherein the first layer of dielectricmaterial defines an outer diameter of the cylindrical tube and thesecond layer of dielectric material defines an inner diameter of thetube; and (ii) a core that at least partially fills an interior of thecylindrical tube defined by the inner diameter of the cylindrical tube.Optionally, the one or more layers of dielectric material are at leastpartially wrapped around the core. Optionally, the one or more layers ofdielectric material are formed as a split cylindrical tube wrappedaround the core, and the split cylindrical tube comprises a gap for thesplit having a predefined width. Optionally, the predefined width isbetween 0.1 mm and 10 mm.

In some embodiments, the first layer of dielectric material comprises atleast one via for each bond pad, and the via comprises a conductivematerial for electrically connecting each bond pad to at least one traceof the subset of conductive traces such that each trace from the subsetof conductive traces terminates at a bond pad.

In some embodiments, the first layer of dielectric material is a hightemperature liquid crystal polymer, and the second layer of dielectricmaterial is a low temperature liquid crystal polymer.

In some embodiments, the core is comprised of one or more layers ofmaterial such that the core has a Shore durometer of greater than 70D.Optionally, the one or more layers of material of the core is polyimide,liquid crystal polymer, parylene, polyether ether ketone, polyurethane,metal, or a combination thereof. Optionally, the one or more layers ofmaterial of the core is thermosetting or thermoplastic polyurethane.

In various embodiments, a monolithic thin-film lead assembly is providedthat comprises: a cable comprising a proximal end, a distal end, asupporting structure that extends from the proximal end to the distalend, and a plurality of conductive traces formed on a portion of thesupporting structure, where the supporting structure is comprised of oneor more layers of dielectric material; an electrode assembly formed onthe supporting structure at the distal end of the cable, where theelectrode assembly comprises one or more electrodes in electricalconnection with one or more conductive traces of the plurality ofconductive traces; and a branched connector formed on the supportingstructure at the proximal end of the cable, where the branched connectorcomprises: (i) a main body comprising the supporting structure and theplurality of conductive traces, and (ii) a plurality of plugs extendingfrom the main body, each plug of the plurality of plugs comprises thesupporting structure and a subset of conductive traces from theplurality of conductive traces, wherein each trace from the subset ofconductive traces terminates at a bond pad exposed on a surface of thesupporting structure.

In some embodiments, the dielectric material is polyimide, liquidcrystal polymer, parylene, polyether ether ketone, or a combinationthereof. In some embodiments, the plurality of conductive traces arecomprised of one or more layers of conductive material, and theconductive material is platinum (Pt), platinum/iridium (Pt/Ir), titanium(Ti), gold/titanium (Au/Ti), or any alloy thereof. Optionally, thesupporting structure of each plug is planar. Optionally, the supportingstructure of each plug is a cylindrical tube.

In some embodiments, the supporting structure of each of the plugscomprises a first layer of dielectric material and a second layer ofdielectric material with the subset of conductive traces buried betweenthe first layer of dielectric material and the second layer ofdielectric material. In some embodiments, each bond pad is a splitannular ring positioned around an axis of the cylindrical tube andexposed on the surface of the cylindrical tube. Optionally, each splitannular ring is spaced apart from one another on the surface of thecylindrical tube by a region of the first layer of the dielectricmaterial.

In some embodiments, the cylindrical tube comprises: (i) the one or morelayers of dielectric material, wherein the first layer of dielectricmaterial defines an outer diameter of the cylindrical tube and thesecond layer of dielectric material defines an inner diameter of thetube; and (ii) a core that at least partially fills an interior of thecylindrical tube defined by the inner diameter of the cylindrical tube.Optionally, the one or more layers of dielectric material are at leastpartially wrapped around the core.

In some embodiments, the one or more layers of dielectric material areformed as a split cylindrical tube wrapped around the core, and thesplit cylindrical tube comprises a gap for the split having a predefinedwidth.

In some embodiments, the first layer of dielectric material comprises atleast one via for each bond pad, and the via comprises a conductivematerial for electrically connecting each bond pad to at least one traceof the subset of conductive traces such that each trace from the subsetof conductive traces terminates at a bond pad. In some embodiments, thefirst layer of dielectric material is a high temperature liquid crystalpolymer, and the second layer of dielectric material is a lowtemperature liquid crystal polymer. Optionally, the core is comprised ofone or more layers of material such that the core has a Shore durometerof greater than 70D.

In various embodiments, a thin-film lead assembly is provided thatcomprises: a cable comprising a proximal end, a distal end, a firstsupporting structure that extends from the proximal end to the distalend, and a plurality of conductive traces formed on a portion of thefirst supporting structure; an electrode assembly formed on the firstsupporting structure at the distal end of the cable, wherein theelectrode assembly comprises one or more electrodes in electricalconnection with one or more conductive traces of the plurality ofconductive traces; and a branched connector comprising: (i) a main bodycomprising a second supporting structure and a plurality of conductiveconnector traces, and (ii) a plurality of plugs extending from the mainbody, each plug of the plurality of plugs comprises the secondsupporting structure and a subset of conductive connecting traces fromthe plurality of conductive connecting traces, where each trace from thesubset of conductive connecting traces terminates at a bond pad exposedon a surface of the second supporting structure, and where the pluralityof conductive connector traces of the branched connector are inelectrical contact with the plurality of conductive traces of the cable,respectively.

In some embodiments, the second supporting structure is comprised of oneor more layers of dielectric material, and the dielectric material ispolyimide, liquid crystal polymer, parylene, polyether ether ketone, ora combination thereof. In some embodiments, the plurality of conductiveconnector traces are comprised of one or more layers of conductivematerial, and the conductive material is platinum (Pt), platinum/iridium(Pt/Ir), titanium (Ti), gold/titanium (Au/Ti), or any alloy thereof.Optionally, the second supporting structure of each plug is planar.Optionally, the second supporting structure of each plug is acylindrical tube.

In some embodiments, the second supporting structure of each of theplugs comprises a first layer of dielectric material and a second layerof dielectric material with the subset of conductive connecting tracesburied between the first layer of dielectric material and the secondlayer of dielectric material. In some embodiments, each bond pad is asplit annular ring positioned around an axis of the cylindrical tube andexposed on the surface of the cylindrical tube. Optionally, each splitannular ring is spaced apart from one another on the surface of thecylindrical tube by a region of the first layer of the dielectricmaterial.

In some embodiments, the cylindrical tube comprises: (i) the one or morelayers of dielectric material, wherein the first layer of dielectricmaterial defines an outer diameter of the cylindrical tube and thesecond layer of dielectric material defines an inner diameter of thetube; and (ii) a core that at least partially fills an interior of thecylindrical tube defined by the inner diameter of the cylindrical tube.

In some embodiments, the one or more layers of dielectric material areat least partially wrapped around the core. Optionally, the one or morelayers of dielectric material are formed as a split cylindrical tubewrapped around the core, and the split cylindrical tube comprises a gapfor the split having a predefined width. Optionally, the first layer ofdielectric material comprises at least one via for each bond pad, andthe via comprises a conductive material for electrically connecting eachbond pad to at least one trace of the subset of conductive connectingtraces such that each trace from the subset of conductive connectingtraces terminates at a bond pad.

In some embodiments, the first layer of dielectric material is a hightemperature liquid crystal polymer, and the second layer of dielectricmaterial is a low temperature liquid crystal polymer. Optionally, thecore is comprised of one or more layers of material such that the corehas a Shore durometer of greater than 70D.

In various embodiments, a neuromodulation system is provided thatcomprises: a neurostimulator comprising an electronics module; a cablecomprising a supporting structure and a plurality of conductive tracesformed on a portion of the supporting structure, where the supportingstructure is comprised of one or more layers of dielectric material; anelectrode assembly formed on the supporting structure, where theelectrode assembly comprises one or more electrodes in electricalconnection with one or more conductive traces of the plurality ofconductive traces; and a branched connector formed on the supportingstructure at the proximal end of the cable, where the branched connectorcomprises: (i) a main body comprising the supporting structure and theplurality of conductive traces, and (ii) a plurality of plugs extendingfrom the main body, each plug of the plurality of plugs comprises thesupporting structure and a subset of conductive traces from theplurality of conductive traces, where the branched connectorelectrically connects each subset of conductive traces from theplurality of conductive traces to the electronics module.

In some embodiments, each trace from the subset of conductive tracesterminates at a bond pad exposed on a surface of the supportingstructure. Optionally, the dielectric material is polyimide, liquidcrystal polymer, parylene, polyether ether ketone, or a combinationthereof. In some embodiments, the plurality of conductive traces arecomprised of one or more layers of conductive material, and theconductive material is platinum (Pt), platinum/iridium (Pt/Ir), titanium(Ti), gold/titanium (Au/Ti), or any alloy thereof. Optionally, thesupporting structure of each plug is planar. Optionally, the supportingstructure of each plug is a cylindrical tube.

In some embodiments, the supporting structure of each of the plugscomprises a first layer of dielectric material and a second layer ofdielectric material with the subset of conductive traces buried betweenthe first layer of dielectric material and the second layer ofdielectric material. Optionally, each bond pad is a split annular ringpositioned around an axis of the cylindrical tube and exposed on thesurface of the cylindrical tube. Optionally, each split annular ring isspaced apart from one another on the surface of the cylindrical tube bya region of the first layer of the dielectric material.

In some embodiments, the cylindrical tube comprises: (i) the one or morelayers of dielectric material, wherein the first layer of dielectricmaterial defines an outer diameter of the cylindrical tube and thesecond layer of dielectric material defines an inner diameter of thetube; and (ii) a core that at least partially fills an interior of thecylindrical tube defined by the inner diameter of the cylindrical tube.Optionally, the one or more layers of dielectric material are at leastpartially wrapped around the core.

In some embodiments, the one or more layers of dielectric material areformed as a split cylindrical tube wrapped around the core, and thesplit cylindrical tube comprises a gap for the split having a predefinedwidth.

In some embodiments, the first layer of dielectric material comprises atleast one via for each bond pad, and the via comprises a conductivematerial for electrically connecting each bond pad to at least one traceof the subset of conductive traces such that each trace from the subsetof conductive traces terminates at a bond pad.

In some embodiments, the first layer of dielectric material is a hightemperature liquid crystal polymer, and the second layer of dielectricmaterial is a low temperature liquid crystal polymer. Optionally, thecore is comprised of one or more layers of material such that the corehas a Shore durometer of greater than 70D.

In various embodiments, a method of manufacturing a branched connectoris provided that comprises: obtaining a flexible printed circuit boardstructure comprising: (i) a main body comprising a supporting structureand a plurality of conductive traces, and (ii) a plurality of plugsextending from the main body, each plug of the plurality of plugscomprises the supporting structure and a subset of conductive tracesfrom the plurality of conductive traces, where each trace from thesubset of conductive traces terminates at a bond pad exposed on asurface of the supporting structure, and wherein the supportingstructure comprise a first polymer layer and a second polymer layer withthe subset of conductive traces buried between the first polymer layerand the second polymer layer; wrapping each of the plurality of plugs atleast partially around a mandrel, respectively, such that each of theplurality of plugs is in a shape of a cylindrical tube; placing a heatshrink tube over each of the plurality of plugs and the mandrels to forma first intermediate structure; heating the first intermediate structureto shrink each of the heat shrink tubes and form a second intermediatestructure; removing the mandrels from the second intermediate structuresuch that each of the plurality of plugs is left with a lumen; injectingthe lumens of the second intermediate structure with a polymer to form athird intermediate structure; heating the third intermediate structureto form the branched connector with a plurality of cylindrical plugs;and removing the heat shrink tubes from the branched connector with theplurality of cylindrical plugs. Each of the plurality of cylindricalplugs comprises the first polymer layer and the second polymer layer atleast partially wrapped around a core made of the polymer.

In some embodiments, the first polymer layer is polyimide, liquidcrystal polymer, parylene, polyether ether ketone, or a combinationthereof. In some embodiments, the second polymer layer is polyimide,liquid crystal polymer, parylene, polyether ether ketone, or acombination thereof. In some embodiments, the plurality of conductivetraces and the subset of conductive traces are comprised of one or morelayers of conductive material, and the conductive material is platinum(Pt), platinum/iridium (Pt/Ir), titanium (Ti), gold/titanium (Au/Ti), orany alloy thereof.

In some embodiments, each of the end portions is partially wrappedaround the mandrel or the polymer tube, respectively such that theplurality of cylindrical end portions are a plurality of splitcylindrical end portions, and each split cylindrical end portion of theplurality of split cylindrical end portions comprises a gap for thesplit having a predefined width.

In some embodiments, the method further comprises forming a thirdpolymer layer on the second polymer layer in a region between the mainbody portion and the plurality of end portions. In some embodiments, thethird polymer layer is silicone.

In various embodiments, a method of manufacturing a branched connectoris provided that comprises: obtaining a flexible printed circuit boardstructure comprising: (i) a main body comprising a supporting structureand a plurality of conductive traces, and (ii) a plurality of plugsextending from the main body, each plug of the plurality of plugscomprises the supporting structure and a subset of conductive tracesfrom the plurality of conductive traces, where each trace from thesubset of conductive traces terminates at a bond pad exposed on asurface of the supporting structure, and wherein the supportingstructure comprise a first polymer layer and a second polymer layer withthe subset of conductive traces buried between the first polymer layerand the second polymer layer; wrapping each of the plurality of plugs atleast partially around a polymer tube, respectively, such that each ofthe plurality of plugs is in a shape of a cylindrical tube; placing aheat shrink tube over each of the plurality of plugs and the polymertubes to form a first intermediate structure; heating the firstintermediate structure with the heat shrink tube to form the branchedconnector with a plurality of cylindrical plugs; and removing the heatshrink tube from the branched connector with the plurality ofcylindrical plugs. The heating embeds each of the plurality of plugsinto the polymer tube, respectively, and each of the plurality ofcylindrical plugs comprises the first polymer layer and the secondpolymer layer at least partially wrapped around a core made of thepolymer tube.

In some embodiments, the first polymer layer is polyimide, liquidcrystal polymer, parylene, polyether ether ketone, or a combinationthereof. In some embodiments, the second polymer layer is polyimide,liquid crystal polymer, parylene, polyether ether ketone, or acombination thereof.

In some embodiments, the plurality of conductive traces and the subsetof conductive traces are comprised of one or more layers of conductivematerial, and the conductive material is platinum (Pt), platinum/iridium(Pt/Ir), titanium (Ti), gold/titanium (Au/Ti), or any alloy thereof.

In some embodiments, each of the end portions is partially wrappedaround the mandrel or the polymer tube, respectively such that theplurality of cylindrical end portions are a plurality of splitcylindrical end portions, and each split cylindrical end portion of theplurality of split cylindrical end portions comprises a gap for thesplit having a predefined width.

In some embodiments, the method further comprises forming a thirdpolymer layer on the second polymer layer in a region between the mainbody portion and the plurality of end portions. In some embodiments, thethird polymer layer is silicone.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood in view of the followingnon-limiting figures, in which:

FIG. 1 shows a neuromodulation system in accordance with variousembodiments;

FIG. 2 shows a lead assembly in accordance with various embodiments;

FIG. 3 shows a branched connector in accordance with variousembodiments;

FIG. 4A shows an enlarged view of the branched connector in accordancewith various embodiments;

FIG. 4B shows a cross-section of the branched connector in accordancewith various embodiments;

FIGS. 5A-5G show an alternative lead assembly in accordance with variousembodiments;

FIGS. 6A-6M show cross-sectional side views and top views illustrating amethod of fabricating a flexible printed circuit board in accordancewith various embodiments;

FIGS. 7A-7H show top views illustrating a method of fabricating abranched connector in accordance with various embodiments; and

FIGS. 8A-8E show top views illustrating an alternative method offabricating a branched connector in accordance with various embodiments.

DETAILED DESCRIPTION

I. Introduction

The following disclosure describes branched proximal connectors for highdensity neural interfaces and methods of microfabricating the branchedproximal connectors. As used herein, the phrase “branched” refers tolateral extensions or subdivisions extending from a main body. As usedherein, the term “proximal” or “proximal end” refers to a first end ofthe main body, while the term “distal” or “distal end” refers to asecond end opposing the first end. For example, the proximal end may bean end of the main body, which is closest to the user, and the distalend may be an end of the main body, which is furthest from the user. Thebranched proximal connector may be fabricated using microfabricatingtechniques. In certain embodiments, the branched connector is fabricatedas a monolithic structure. As used herein, the phrase “monolithic”refers to a device fabricated using a same layer of base material. Asused herein, the phrase “microfabrication” refers to the process offabricating miniature structures on micrometer scales and smaller. Themajor concepts and principles of microfabrication are microlithography,doping, thin films, etching, bonding, and polishing. As used herein, thephrase “thin films” refers to a layer of material ranging from fractionsof a nanometer (monolayer) to several micrometers in thickness (e.g.,between a few nanometers to about 100 μm). Thin films may be depositedby applying a very thin film of material (e.g., between a few nanometersto about 100 μm) onto a substrate surface to be coated, or onto apreviously deposited layer of thin film. In various embodiments, a thinfilm connector is provided comprising a base polymer body (e.g., asupporting structure) and at least one conductive trace formed on thebase polymer body. As used herein, the term “high density neuralinterface(s)” refers to a neural interface that comprises at leastsixteen electrodes (i.e., recording, sensing, stimulating, other typesof electrodes, or combinations thereof).

Neuromodulation devices such as deep brain and spinal cord stimulatorselectrically interface with neural tissue and treat various neurologicalconditions through electrical stimulation. As described herein,conventional neuromodulation devices use between four and sixteenelectrodes and comprise a neurostimulator and lead assembly containingelectrodes. There is a need for high-density lead assemblies that cansignificantly increase the number of electrodes in order to interfacewith larger tissue volume, to recruit smaller populations of neurons forrecording, or to provide more targeted therapy by tailoring theelectrical stimulation parameters and activated tissue volume.Conventional neuromodulation devices use up to eight channels per leadassembly in an axial orientation. These devices are typically limited tono more than eight channels per lead assembly due partly to the lack ofcompatible connector technology. Conventional neuromodulation devicesthat can accommodate greater than eight channels per lead assembly arelimited by a requirement of permanency of the connection to limitsusceptibility of the connector to disconnections and fractures.

To address these limitations and problems, branched proximal connectorsof various embodiments disclosed herein enable connections with highdensity neural interfaces and are capable of being physicallydisconnected between the neurostimulator and the lead assembly. Oneillustrative embodiment of the present disclosure is directed to abranched connector that includes a main body having a base portion of asupporting structure and a plurality of conductive traces formed on thebase portion, and a plurality of plugs extending from the main body. Thebase portion of the supporting structure is comprised of one or morelayers of dielectric material. Each plug of the plurality of plugsincludes an end portion of the supporting structure comprised of the oneor more layers of dielectric material, and a subset of conductive tracesfrom the plurality of conductive traces. Each trace from the subset ofconductive traces terminates at a bond pad exposed on a surface of theend portion of the supporting structure.

In other embodiments, a monolithic thin-film lead assembly is providedthat includes a cable comprising a proximal end, a distal end, asupporting structure that extends from the proximal end to the distalend, and a plurality of conductive traces formed on a portion of thesupporting structure. The supporting structure is comprised of one ormore layers of dielectric material. The monolithic thin-film leadassembly further includes an electrode assembly formed on the supportingstructure at the distal end of the cable. The electrode assemblycomprises one or more electrodes in electrical connection with one ormore conductive traces of the plurality of conductive traces. Themonolithic thin-film lead assembly further includes a branched connectorformed on the supporting structure at the proximal end of the cable. Thebranched connector comprises: (i) a main body comprising the supportingstructure and the plurality of conductive traces, and (ii) a pluralityof plugs extending from the main body, each plug of the plurality ofplugs comprises the supporting structure and a subset of conductivetraces from the plurality of conductive traces, where each trace fromthe subset of conductive traces terminates at a bond pad exposed on asurface of the supporting structure.

In other embodiments, a thin-film lead assembly is provided thatincludes a cable comprising a proximal end, a distal end, a firstsupporting structure that extends from the proximal end to the distalend, and a plurality of conductive traces formed on a portion of thefirst supporting structure. The thin-film lead assembly further includesan electrode assembly formed on the first supporting structure at thedistal end of the cable. The electrode assembly comprises one or moreelectrodes in electrical connection with one or more conductive tracesof the plurality of conductive traces. The thin-film lead assemblyfurther includes a branched connector comprising: (i) a main bodycomprising a second supporting structure and a plurality of conductiveconnector traces, and (ii) a plurality of plugs extending from the mainbody, each plug of the plurality of plugs comprises the secondsupporting structure and a subset of conductive connecting traces fromthe plurality of conductive connecting traces. Each trace from thesubset of conductive connecting traces terminates at a bond pad exposedon a surface of the second supporting structure. The plurality ofconductive connector traces of the branched connector are in electricalcontact with the plurality of conductive traces of the cable,respectively.

In other embodiments, a neuromodulation system is provided that includesa neurostimulator comprising an electronics module, a cable comprising asupporting structure and a plurality of conductive traces formed on aportion of the supporting structure, where the supporting structure iscomprised of one or more layers of dielectric material, an electrodeassembly formed on the supporting structure, where the electrodeassembly comprises one or more electrodes in electrical connection withone or more conductive traces of the plurality of conductive traces, anda branched connector formed on the supporting structure at the proximalend of the cable. The branched connector comprises: (i) a main bodycomprising the supporting structure and the plurality of conductivetraces, and (ii) a plurality of plugs extending from the main body, eachplug of the plurality of plugs comprises the supporting structure and asubset of conductive traces from the plurality of conductive traces. Thebranched connector electrically connects each subset of conductivetraces from the plurality of conductive traces to the electronicsmodule.

To further address these limitations and problems, a method ofmanufacturing the branched connector of various embodiments disclosedherein includes process steps for creating a branched structure, whichresults in increased contact points, a smaller footprint, and greaterdesign flexibility. One illustrative embodiment of the presentdisclosure is directed to a method of manufacturing a branched connectorthat comprises forming a first polymer layer on a substrate. The firstpolymer layer comprises a main body portion and a plurality of endportions extending from the main body portion, and the main body portionand the plurality of end portions are co-planar. The method furthercomprises forming a plurality of conductive traces on the main bodyportion in a first pattern. The first pattern maintains a firstpredetermined distance between each trace of the plurality of traces.The method further comprises forming a subset of conductive traces oneach of the plurality of end portions in a second pattern. The secondpattern maintains a second predetermined distance between each trace ofthe subset of traces and electrical connects each trace of the subset oftraces to each trace of the plurality of traces, respectively. Themethod further comprises depositing a second polymer layer on the firstpolymer layer, the plurality of conductive traces, and each of thesubset of conductive traces. The method further comprises forming atleast one contact via in the first polymer layer of each of theplurality of end portions such that the at least one contact via is inelectrical contact with at least one trace of the subset of conductivetraces. The method further comprises forming at least on bond pad on thefirst polymer layer of each of the plurality of end portions such thatthe at least one bond pad is in electrical contact with the at least onecontact via, and cutting the branched connector from the first polymerlayer and the second polymer. The branched connector comprises the mainbody portion and the plurality of end portions extending from the mainbody portion.

Advantageously, these approaches provide a branched connector, which hasincreased contact points, a smaller footprint, and greater designflexibility. More specifically, these approaches enable branchedconnectors with reliable, non-permanent connections between a leadassembly and a neurostimulator. This solution is scalable to connectingmany electrodes (e.g., greater than sixteen) using a multi flex chip,and thus enabling several therapeutic opportunities forneurostimulation. Furthermore even for applications where multipleelectrodes are not required, various embodiments can be miniaturized tomake the implant minimally invasive, additionally may make invasiveanatomies to become accessible (or navigable) due to theminiaturization. It should be understood that although deep brainneurostimulation and vagus nerve or artery/nerve plexus deviceapplications are provided as examples of some embodiments, this solutionis applicable to all leads and devices that need electrodes/sensors thatneed to be attached to a neurostimulator.

II. Neuromodulation Devices and Systems with a Lead Assembly

FIG. 1 shows a neuromodulation system 100 in accordance with someaspects of the present invention. In various embodiments, theneuromodulation system 100 includes an implantable neurostimulator 105and a lead assembly 110. The implantable neurostimulator 105 (e.g., animplantable pulse generator (IPG)) may include a housing 115, afeedthrough assembly 120, a power source 125, an antenna 130, and anelectronics module 135 (e.g., a computing system). The housing 115 maybe comprised of materials that are biocompatible such as bioceramics orbioglasses for radio frequency transparency, or metals such as titanium.In accordance with some aspects of the present invention, the size andshape of the housing 115 may be selected such that the neurostimulator105 can be implanted within a patient. In the example shown in FIG. 1,the feedthrough assembly 120 is attached to a hole in a surface of thehousing 115 such that the housing 115 is hermetically sealed. Thefeedthrough assembly 120 may include one or more contacts (i.e.,electrically conductive elements, pins, wires, tabs, pads, etc.) mountedwithin the housing 115 or a cap extending from an interior to anexterior of the housing 115. The power source 125 may be within thehousing 115 and connected (e.g., electrically connected) to theelectronics module 135 to power and operate the components of theelectronics module 135. The antenna 130 may be connected (e.g.,electrically connected) to the electronics module 135 for wirelesscommunication with external devices via, for example, radiofrequency(RF) telemetry.

In some embodiments, the electronics module 135 may be connected (e.g.,electrically connected) to interior ends of the feedthrough assembly 120such that the electronics module 135 is able to apply a signal orelectrical current to conductive traces of the lead assembly 110connected to the feedthrough assembly 120. The electronics module 135may include discrete and/or integrated electronic circuit componentsthat implement analog and/or digital circuits capable of producing thefunctions attributed to the neuromodulation devices or systems such asapplying or delivering neural stimulation to a patient. In variousembodiments, the electronics module 135 may include software and/orelectronic circuit components such as a pulse generator 140 thatgenerates a signal to deliver a voltage, current, optical, or ultrasonicstimulation to a nerve or artery/nerve plexus via electrodes, acontroller 145 that determines or senses electrical activity andphysiological responses via the electrodes and sensors, controlsstimulation parameters of the pulse generator 140 (e.g., controlstimulation parameters based on feedback from the physiologicalresponses), and/or causes delivery of the stimulation via the pulsegenerator 140 and electrodes, and a memory 150 with program instructionsoperable on by the pulse generator 140 and the controller 145 to performone or more processes for applying or delivering neural stimulation.

In various embodiments, the lead assembly 110 includes a cable or leadbody 155, one or more electrode assemblies 160 having one or moreelectrodes 165 (optionally one or more sensors), and a branchedconnector 170. In some embodiments, the lead assembly 110 is amonolithic structure. In various embodiments, the branched connector 170includes a main body 175 having a base portion of a supporting structure177 and one or more of conductive traces 180 formed on the base portion,and a plurality of plugs 182 extending from the main body. The baseportion of the supporting structure may be comprised of one or morelayers of dielectric material. Each plug of the plurality of plugsincludes an end portion of the supporting structure comprised of the oneor more layers of dielectric material, and a subset of conductive traces185 from the one or more of conductive traces. Each trace from thesubset of conductive traces terminates at a bond pad exposed on asurface of the end portion of the supporting structure.

The cable 155 may include one or more conductive traces 190 formed on asupporting structure 195. The one or more conductive traces 190 allowfor electrical coupling of the electronics module 135 to the electrodes165 and/or sensors of the electrode assemblies 160 via the branchedconnector 170. In some embodiments, the one or more of conductive traces180 are the same conductive traces as the one or more conductive traces190 (monolithic traces). In other embodiments, the one or more ofconductive traces 180 are different conductive traces from the one ormore conductive traces 190 (a different structure but electricallyconnected). As described herein in detail, the supporting structure177/195 may be formed with a dielectric material such as a polymerhaving suitable dielectric, flexibility and biocompatibilitycharacteristics. Polyurethane, polycarbonate, silicone, polyethylene,fluoropolymer and/or other medical polymers, copolymers and combinationsor blends may be used. The conductive material for the traces 180/190may be any suitable conductor such as stainless steel, silver, copper orother conductive materials, which may have separate coatings orsheathing for anticorrosive, insulative and/or protective reasons.

The electrode assemblies 160 may include the electrodes 165 and/orsensors fabricated using various shapes and patterns to create certaintypes of electrode assemblies (e.g., book electrodes, split cuffelectrodes, spiral cuff electrodes, epidural electrodes, helicalelectrodes, probe electrodes, linear electrodes, neural probe, paddleelectrodes, intraneural electrodes, etc.). In various embodiments, theelectrode assemblies 160 include a base material that provides supportfor microelectronic structures including the electrodes 165, a wiringlayer, optional contacts, etc. In some embodiments, the base material isthe supporting structure 195. The wiring layer may be embedded within orlocated on a surface of the supporting structure 195. The wiring layermay be used to electrically connect the electrodes 165 with the one ormore conductive traces 190 directly or indirectly via a lead conductor.The term “directly”, as used herein, may be defined as being withoutsomething in between. The term “indirectly”, as used herein, may bedefined as having something in between. In some embodiments, theelectrodes 165 may make electrical contact with the wiring layer byusing the contacts.

III. Branched Connectors

FIG. 2 shows a lead assembly 200 (e.g., the lead assembly 110 describedwith respect to FIG. 1) in accordance with aspects of the presentdisclosure. In various embodiments, the lead assembly 200 comprises acable 205 having a proximal end 210 and a distal end 215. The cable 205may comprise a supporting structure 220 and a plurality of conductivetraces 225 formed on a portion of the supporting structure 220. As usedherein, the term “formed on” refers to a structure or feature that isformed on a surface of another structure or feature, a structure orfeature that is formed within another structure or feature, or astructure or feature that is formed both on and within another structureor feature. In some embodiments, the supporting structure 220 extendsfrom the proximal end 210 to the distal end 215. In some embodiments,the supporting structure 220 may be made of one or more layers ofdielectric material (i.e., an insulator). The dielectric material may beselected from the group of electrically flexible nonconductive materialsconsisting of organic or inorganic polymers, polyimide-epoxy,epoxy-fiberglass, and the like. In certain embodiments, the dielectricmaterial is a polymer of imide monomers (i.e., a polyimide), a liquidcrystal polymer (LCP) such as Kevlar®, parylene, polyether ether ketone(PEEK), or combinations thereof. In other embodiments, the supportingstructure 220 may be made of one or more layers of dielectric materialformed on a substrate. The substrate may be made from any type ofmetallic or non-metallic material.

In various embodiments, the one or more conductive traces 225 are aplurality of traces, for example, two or more conductive traces or fromtwo to twenty-four conductive traces. The plurality of conductive traces225 are comprised of one or more layers of conductive material. Theconductive material selected for the one or more conductive traces 225should have good electrical conductivity and may include pure metals,metal alloys, combinations of metals and dielectrics, and the like. Forexample, the conductive material may be platinum (Pt), platinum/iridium(Pt/Ir), titanium (Ti), gold/titanium (Au/Ti), or any alloy thereof. Insome embodiments, it is also desirable that the conductive materialselected for the one or more conductive traces 225 have thermalexpansion characteristics or a coefficient of thermal expansion (CTE)that is approximately equal to that of CTE of the supporting structure220. Matching the CTE of components that contact one another isdesirable because it eliminates the development of thermal stresses,which may occur during fabrication and the operation of the cable, andthus eliminates a known cause of mechanical failure in the components.

As shown in FIG. 2, the lead assembly 200 may further comprise anelectrode assembly 230 formed on a supporting structure 235. Thesupporting structure 235 may provide support for microelectronicstructures including one or more electrodes 240, a wiring layer 245, andoptional contact(s) (not shown). The electrode assembly 230 may belocated at the distal end 215 of the lead assembly 200. The one or moreelectrodes 240 are in electrical connection with one or more conductivetraces of the plurality of conductive traces 225, for example, via thewiring layer 245 and optionally the contact(s). In various embodiments,the supporting structure 220 of the cable 205 and the supportingstructure 235 of the electrode assembly 230 are the same structure(i.e., the supporting structure is continuous from the proximal end 210to the distal end 215), which thus creates a monolithic cable. Inalternative embodiments, the supporting structure 220 of the cable 205and the supporting structure 235 of the electrode assembly 230 aredifferent structures but are connected such that there is an electricalconnection between the plurality of conductive traces 225, wiring layer245, and the one or more electrodes 240.

As shown in FIG. 2, the lead assembly 200 may further comprise abranched connector 255 formed on a supporting structure 260. Thebranched connector 255 may comprise a main body 265 comprising a baseportion 270 of the supporting structure 260 and one or more conductivetraces 275 formed on the base portion 270. The base portion 270 of thesupporting structure 260 may be comprised of one or more layers ofdielectric material. In some embodiments, the supporting structure 260may be made of one or more layers of dielectric material (i.e., aninsulator). The dielectric material may be selected from the group ofelectrically flexible nonconductive materials consisting of organic orinorganic polymers, polyimide-epoxy, epoxy-fiberglass, and the like. Incertain embodiments, the dielectric material is a polymer of imidemonomers (i.e., a polyimide), a liquid crystal polymer (LCP) such asKevlar®, parylene, polyether ether ketone (PEEK), or combinationsthereof. In other embodiments, the supporting structure 260 may be madeof one or more layers of dielectric material formed on a substrate. Thesubstrate may be made from any type of metallic or non-metallicmaterial. In various embodiments, the supporting structure 220 of thecable 205 and the supporting structure 260 of the branched connector 255are the same structure (i.e., the supporting structure is continuousfrom the proximal end 210 to the distal end 215), which thus creates amonolithic cable. In alternative embodiments, the supporting structure220 of the cable 205 and the supporting structure 260 of the branchedconnector 255 are different structures but are connected such that thereis an electrical connection between the plurality of conductive traces225, wiring layer 245, the one or more electrodes 240, and the one ormore conductive traces 275.

In various embodiments, the one or more conductive traces 275 are aplurality of traces, for example, two or more conductive traces or fromtwo to twenty-four conductive traces. The plurality of conductive traces275 are comprised of one or more layers of conductive material. Theconductive material selected for the one or more conductive traces 275should have good electrical conductivity and may include pure metals,metal alloys, combinations of metals and dielectrics, and the like. Forexample, the conductive material may be platinum (Pt), platinum/iridium(Pt/Ir), titanium (Ti), gold/titanium (Au/Ti), or any alloy thereof. Insome embodiments, it is also desirable that the conductive materialselected for the one or more conductive traces 275 have thermalexpansion characteristics or a coefficient of thermal expansion (CTE)that is approximately equal to that of CTE of the supporting structure260. Matching the CTE of components that contact one another isdesirable because it eliminates the development of thermal stresses,which may occur during fabrication and the operation of the cable, andthus eliminates a known cause of mechanical failure in the components.As used herein, the terms “substantially,” “approximately” and “about”are defined as being largely but not necessarily wholly what isspecified (and include wholly what is specified) as understood by one ofordinary skill in the art. In any disclosed embodiment, the term“substantially,” “approximately,” or “about” may be substituted with“within [a percentage] of” what is specified, where the percentageincludes 0.1, 1, 5, and 10 percent.

The branched connector 255 may further comprise a plurality of plugs 280extending from the main body 265. In some embodiments, at least one plugof the plurality of plugs 280 comprises an end portion 285 of thesupporting structure 260 comprised of the one or more layers ofdielectric material, and a subset of conductive traces 290 from theplurality of conductive traces 275. The base portion 270 of thesupporting structure 260 and each of the end portions 285 of thesupporting structure 260 may be monolithic. At least one trace from thesubset of conductive traces 290 may terminate at a bond pad 295 exposedon a surface of the end portion 285 of the supporting structure. Inalternative embodiments, each plug of the plurality of plugs 280comprises an end portion 285 of the supporting structure 260 comprisedof the one or more layers of dielectric material, and a subset ofconductive traces 290 from the plurality of conductive traces 275. Eachtrace from the subset of conductive traces 290 may terminate at a bondpad 295 exposed on a surface of the end portion 285 of the supportingstructure. As should be understood, in some embodiments, each electrodefrom the one or more electrodes 240 is electrically connected via acorresponding wiring layer 245, optional contact, conductive trace 225,conductive trace 275, subset conductive trace 290, and bond pad 295 to arespective bond pad. In other words, each electrode may be electricallyconnected to a different bond pad (a one to one relationship). Inalternative embodiments, a multiplexer chip may be used such that one ormore electrodes from the one or more electrodes 240 is electricallyconnected via wiring layer 245, optional contact, a conductive trace225, a conductive trace 275, and a subset conductive trace 290 to asingle bond pad 295. In other words, each electrode may be electricallyconnected to a same or different bond pad (a many to one relationship).

The one or more conductive traces 275 and subset of conductive traces290 may be deposited onto a surface of the supporting structure 260 byusing thin film deposition techniques well known to those skilled in theart such as by sputter deposition, chemical vapor deposition, metalorganic chemical vapor deposition, electroplating, electroless plating,and the like. In some embodiments, the thickness of the one or moreconductive traces 275 and subset of conductive traces 290 is dependenton the particular impedance desired for conductor, in order to ensureexcellent signal integrity (e.g., electrical signal integrity forstimulation or recording). For example, if a conductor having arelatively high impedance is desired, a small thickness of conductivematerial should be deposited onto the supporting structure 260. If,however, a signal plane having a relatively low impedance is desired, agreater thickness of electrically conductive material should bedeposited onto the supporting structure 260. In certain embodiments,each of the one or more conductive traces 275 and subset of conductivetraces 290 has a thickness (t). In some embodiments, the thickness (t)is from 0.5 μm to 25 μm or from 5 μm to 10 μm, for example about 5 μm orabout 8 μm. In some embodiments, each of the one or more conductivetraces 275 and subset of conductive traces 290 has a length (l) of about1 mm to 100 mm or 1 cm to 3 cm, e.g., about 15 mm. In some embodiments,each of the one or more conductive traces 275 and subset of conductivetraces 290 has a width (w) from 2.0 μm to 500 μm, for example about 30μm or about 50 μm.

As shown in FIG. 3, the branched connector 300 (e.g., the branchedconnector 255 as discussed with respect to FIG. 2) may be formed on asupporting structure 305 at the proximal end 310 of a cable 315 with apredetermined shape in accordance with aspects of the presentdisclosure. In particular, as described in greater detail herein, thebranched connector 300 may be formed with a predetermined shape from aprefabricated wafer or panel of dielectric material or optionally asubstrate. For example, the branched connector 300 may be laser cut froma prefabricated wafer or panel in a bifurcated or multi-branched shape.Two branches are shown (bifurcated) in some of the figures but it shouldbe understood that more than two branches can be used (multi-branched).The bifurcated or multi-branched shape may include characteristicsdesigned to minimize the footprint of the connector while maximizing thenumber of contacts or bond pads that can be fabricated for theconnector.

In some embodiments, as shown in FIG. 4A, the branched connector 400 maybe formed on a supporting structure 405 at the proximal end 410 of acable 415. The branched connector 400 may comprise: (i) a main body 420comprising the supporting structure 405 and a plurality of conductivetraces 425, and (ii) a plurality of plugs 430 extending from the mainbody 420. Each plug of the plurality of plugs 430 may comprise thesupporting structure 405 and a subset of conductive traces 435 from theplurality of conductive traces 425. Each trace from the subset ofconductive traces 435 may terminate at a bond pad 440 exposed on asurface 445 of the supporting structure 405. As illustrated in FIG. 4A,one or more of the plugs 430 (or ends of the supporting structure) areplanar. In some embodiments, each of the plugs 430 (or ends of thesupporting structure) are planar. A used herein, “planar” means relatingto or in the form of a plane. In some embodiments, two or more of theplugs 430 (or ends of the supporting structure) are coplanar with oneanother. In some embodiments, one or more of the plugs 430 (or ends ofthe supporting structure) are coplanar with the main body. As usedherein, “coplanar” means in the same plane.

As shown in FIG. 4B (cross-section of a plug 430 along X-X from FIG.4A), the supporting structure 405 of each of the plugs 430 comprises afirst layer of dielectric material 450 and a second layer of dielectricmaterial 455 with the subset of conductive traces 435 buried between thefirst layer of dielectric material 450 and the second layer ofdielectric material 455. In some embodiments, the first layer ofdielectric material 450 comprises at least one contact via 460 for eachbond pad 440. The contact via 460 may comprise a conductive material forelectrically connecting each bond pad 440 to at least one trace of thesubset of conductive traces 435 such that each trace from the subset ofconductive traces 435 terminates at a bond pad 440. The contact via 460may be connected to the at least one trace of the subset of conductivetraces 435 directly or indirectly by way of a wiring layer (not shown).In some embodiments, the conductive material is lined on at least aportion of the walls of the via hole. In other embodiments, theconductive material fills the via hole. In some embodiments, the firstlayer of dielectric material 450 is a high temperature liquid crystalpolymer, and the second layer of dielectric material 455 is a lowtemperature liquid crystal polymer. As used herein, “a high temperatureliquid crystal polymer” refers to a liquid crystal polymer with a highmelting temperature of greater than 300° C. As used herein, “a lowtemperature liquid crystal polymer” refers to a liquid crystal polymerwith a low melting temperature of less than 300° C. In otherembodiments, as shown in FIGS. 5A, 5B, 5C, 5F, and 5G, the branchedconnector 500 may be formed on a supporting structure 505 at theproximal end 510 of a cable 515. The branched connector 500 maycomprise: (i) a main body 520 comprising the supporting structure 505and a plurality of conductive traces 525, and (ii) a plurality of plugs530 extending from the main body 520. Each plug of the plurality ofplugs 530 may comprise the supporting structure 505 and a subset ofconductive traces 535 from the plurality of conductive traces 525. Eachtrace from the subset of conductive traces 535 may terminate at a bondpad 540 exposed on a surface 545 of the supporting structure 505. Asillustrated in FIG. 5F, one or more of the plugs 530 (or ends of thesupporting structure) are a cylindrical tube 565. Although the plugs aredescribed herein with respect to a cylindrical tube shape, it should beunderstood that other shapes for the plugs have been contemplated, forexample, spherical cubed, torus, ellipsoid, etc. In some embodiments,each of the plugs 530 (or ends of the supporting structure) is acylindrical tube 565. A used herein, “cylindrical” means having straightparallel sides and a circular or oval cross-section; in the shape orform of a cylinder.

As shown in FIG. 5G (cross-section of a plug 530 along Y-Y from FIG.5B), the supporting structure 505 of each of the plugs 530 comprises afirst layer of dielectric material 550 and a second layer of dielectricmaterial 555 with the subset of conductive traces 535 buried between thefirst layer of dielectric material 550 and the second layer ofdielectric material 555. In some embodiments, the first layer ofdielectric material 550 comprises at least one via contact 560 for eachbond pad 540. The via contact 560 may comprise a conductive material forelectrically connecting each bond pad 540 to at least one trace of thesubset of conductive traces 530 such that each trace from the subset ofconductive traces 530 terminates at a bond pad 540. The via contact 560may be connected to the at least one trace of the subset of conductivetraces 530 directly or indirectly by way of a wiring layer (not shown).In some embodiments, the conductive material is line on at least aportion of the walls of the via hole. In other embodiments, theconductive material fills the via hole. In some embodiments, the firstlayer of dielectric material 550 is a high temperature liquid crystalpolymer, and the second layer of dielectric material 555 is a lowtemperature liquid crystal polymer.

As shown in FIG. 5F, cylindrical tube 565 comprises the one or morelayers of dielectric material 550/555. The first layer of dielectricmaterial 550 may define an outer diameter (d) of the cylindrical tube565 and the second layer of dielectric material 555 may define an innerdiameter (d′) of the tube. The cylindrical tube 565 may further comprisea core 570 that at least partially fills an interior of the cylindricaltube 565 defined by the inner diameter (d′) of the cylindrical tube 565.The core 570 may be comprised of one or more layers of material suchthat the core 570 has a Shore durometer of greater than 70D. In someembodiments, the one or more layers of material of the core 570 ispolyimide, liquid crystal polymer, parylene, polyether ether ketone,polyurethane, metal, or a combination thereof. In certain embodiments,the one or more layers of material of the core 570 is a thermosetting orthermoplastic polyurethane. The one or more layers of dielectricmaterial 550/555 may be at least partially wrapped around the core 570.In certain embodiments, the one or more layers of dielectric material550/555 are formed as a split cylindrical tube wrapped around the core570, and the split cylindrical tube comprises a gap 575 for the splithaving a predefined width (z). The predefined width may be between 0.1mm and 10 mm, for example about 2 mm.

As shown in FIGS. 5A, 5B, 5C, and 5F, in some embodiments, the one ormore of the bond pads 540 are a split annular ring positioned around anaxis 580 of the cylindrical tube 565 and exposed on the surface 585 ofthe cylindrical tube 565. Each split annular ring may spaced apart fromone another on the surface 585 of the cylindrical tube 565 by a region590 of the first layer of the dielectric material 550. A width (p) ofthe region 590 of the first layer of the dielectric material 550 thatseparates each split annular ring may be between 1.0 mm to 10 mm, forexample about 3 mm. In some embodiments, each split annular ringconnects to a single trace from the subset of conductive traces 530. Inother embodiments, each split annular ring connects to two or moretraces from the subset of conductive traces 530. For example, a leftside of the split annular ring may be connected with a first trace and aright side of the annular ring may be connected with a second trace.Alternatively, a multiplexer chip may be used to drive signals and thusthe split annular ring may be connected to multiple traces from theconductive traces 530. In various embodiments, eight bond pads 540 orsplit annular rings are positioned around the axis 580 of eachcylindrical tube 565 and exposed on the surface 585 of each cylindricaltube 565; however, it should be understood that more or less than eightbond pads 540 or split annular rings can be positioned on thecylindrical tubes 565. For example, each cylindrical tube 565 can havethe same or a different amount of bond pads 540 or split annular rings(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, etc.) to enhance design flexibilityfor the branched connector 500.

As shown in FIGS. 5A-5F, in various embodiments, the branched connector500 may be part of a monolithic thin-film lead assembly 592 thatcomprises the cable 515 and an electrode assembly 594 (e.g., the cable205 and electrode assembly 230 discussed with respect to FIG. 2). Insome embodiments, the supporting structure of the cable 593 and thesupporting structure of the branched connector 255 are the samestructure (i.e., the supporting structure is continuous from theproximal end 210 to the distal end 215), which thus creates a monolithiccable. The branched connector 500 may include a stylet lumen 595 that iseither integral with a lumen of the cable 593 or a connected extensionof the lumen of the cable 593. The stylet lumen 595 providescompatibility with existing surgical techniques where a lead assembly592 is implanted by sliding a rigid stylet through the center of thecable 593.

While the branched connectors have been described at some length andwith some particularity with respect to a specific design and/orperformance need, it is not intended that the branched connectors belimited to any such particular design and/or performance need. Instead,it should be understood the branched connectors described herein areexemplary embodiments, and that the branched connectors are to beconstrued with the broadest sense to include variations of the specificdesign and/or performance need described herein, as well as othervariations that are well known to those of skill in the art. Inparticular, the shape and location of components and layers in thebranched connectors may be adjusted or modified to meet specific designand/or performance needs. Furthermore, it is to be understood that otherstructures have been omitted from the description of the branchedconnectors for clarity. The omitted structures may include insulatinglayers, interconnect components, passive devices, etc.

IV. Methods for Fabricating Branched Connectors

FIGS. 6A-6M show structures and respective processing steps forfabricating a flexible printed circuit board 600 (e.g., as describedwith respect to FIGS. 2, 3, 4A, 4B, and 5A-5G) in accordance withvarious aspects of the invention. It should be understood by those ofskill in the art that the flexible printed circuit board 600 can bemanufactured in a number of ways using a number of different tools. Ingeneral, however, the methodologies and tools used to form thestructures of the various embodiments can be adopted from integratedcircuit (IC) technology. For example, the structures of the variousembodiments, e.g., supporting structure, conductive traces, electrodes,sensors, wiring layers, bond/contact pads, etc., may be built with orwithout a substrate and realized in films of materials patterned byphotolithographic processes. In particular, the fabrication of variousstructures described herein may typically use three basic buildingblocks: (i) deposition of films of material on a substrate and/orprevious film(s), (ii) applying a patterned mask on top of the film(s)by photolithographic imaging, and (iii) etching the film(s) selectivelyto the mask.

As used herein, the term “depositing” may include any known or laterdeveloped techniques appropriate for the material to be depositedincluding but not limited to, for example: chemical vapor deposition(CVD), low-pressure CVD (LPCVD), plasma-enhanced CVD (PECVD),semi-atmosphere CVD (SACVD) and high density plasma CVD (HDPCVD), rapidthermal CVD (RTCVD), ultra-high vacuum CVD (UHVCVD), limited reactionprocessing CVD (LRPCVD), metalorganic CVD (MOCVD), sputteringdeposition, ion beam deposition, electron beam deposition, laserassisted deposition, thermal oxidation, thermal nitridation, spin-onmethods, physical vapor deposition (PVD), atomic layer deposition (ALD),chemical oxidation, molecular beam epitaxy (MBE), plating (e.g.,electroplating), or evaporation.

FIG. 6A shows a cross-section of a beginning structure (a supportingstructure) comprising a first polymer layer 605 overlying an optionalsubstrate 610 (e.g., a backer). In some embodiments, the beginningstructure may be provided, obtained, or fabricated as a single wafer orpanel having a diameter, length, and/or width of less than 15 cm. Inother embodiments, the beginning structure may be provided, obtained, orfabricated for a reel-to-reel process where the substrate is long andbig to reduce costs. For example, panels may be used that are at least20×23 cm rectangles. The substrate 610 may be comprised of any type ofmetallic or non-metallic material. For example, the substrate 610 may becomprised of but not limited to silicon, germanium, silicon germanium,silicon carbide, and those materials consisting essentially of one ormore Group III-V compound semiconductors having a composition defined bythe formula AlX1GaX2InX3AsY1PY2NY3SbY4, where X1, X2, X3, Y1, Y2, Y3,and Y4 represent relative proportions, each greater than or equal tozero and X1+X2+X3+Y1+Y2+Y3+Y4=1 (1 being the total relative molequantity). Substrate 610 may additionally or alternatively be comprisedof Group II-VI compound semiconductors having a compositionZnA1CdA2SeB1TeB2, where A1, A2, B1, and B2 are relative proportions eachgreater than or equal to zero and A1+A2+B1+B2=1 (1 being a total molequantity). The processes to provide, obtain, or fabricate substrate 610,as illustrated and described, are well known in the art and thus, nofurther description is provided herein.

The first polymer layer 605 may be comprised of dielectric material(i.e., an insulator). The dielectric material may be selected from thegroup of electrically flexible nonconductive materials consisting oforganic or inorganic polymers, polyimide-epoxy, epoxy-fiberglass, andthe like. In certain embodiments, the dielectric material is athermoplastic or thermosetting polymer. For example, the polymer may bea polyimide, a LCP, parylene, a PEEK, or combinations thereof. Theforming of the first polymer layer 605 may include depositing and curinga dielectric material directly on the substrate 610 without an adhesionpromoter. For example, a solution comprised of an imidizable polyamicacid compound dissolved in a vaporizable organic solvent without anadhesion promoter may be deposited (e.g., spin coated) onto thesubstrate 610. The solution may then be heated at a temperature,preferably less than 250° C., to imidize the polyamic acid compound toform the desired polyimide and vaporize the solvent. The first polymerlayer 605 may then be thinned to a desired thickness by planarization,grinding, wet etch, dry etch, oxidation followed by oxide etch, or anycombination thereof. This process can be repeated to achieve a desiredthickness for the first polymer layer 605. In some embodiments, thefirst polymer layer 605 may have a thickness from 10 μm to 150 μm. Insome embodiments, the first polymer layer 605 may have a thickness from25 μm to 100 μm. In some embodiments, the first polymer layer 605 mayhave a thickness from 35 μm to 75 μm. FIG. 6B shows a top view of thebeginning structure, which illustrates the first polymer layer 605 maycomprise a main body portion 615 and a plurality of end portions 620extending from the main body portion 605. In some embodiments, the mainbody portion 615 and the plurality of end portions 620 are coplanar.

FIG. 6C shows conductive traces 625 formed in a first pattern on themain body portion 615 of the first polymer layer 605. In someembodiments, forming the conductive traces 625 includes depositing aseed layer (e.g., a platinum (Pt) seed layer, platinum/iridium (Pt/Ir)seed layer, etc.) over the first polymer layer 605. The seed layer maybe configured to enable forming of a conductive trace on the firstpolymer layer 605 (e.g., through platinum (Pt) electroplating,platinum/iridium (Pt/Ir) electroplating, etc.). Optionally, and prior toforming of the seed layer, an adhesion layer may be deposited over thefirst polymer layer 605 to enable adequate application of the seedlayer. Deposition of either or both of the adhesion layer and seed layermay include sputter deposition

Following deposition of the seed layer, a resist pattern may be formedabove the first polymer layer 605. The resist pattern may includeopenings that align over at least a portion of the first polymer layer605 for forming of a plurality of conductive traces 625 (e.g., aconductive layer with a cross-sectional thickness of 0.5 μm to 100 μm orfrom 25 μm to 50 μm) on the first polymer layer 605. For example, theresist may be patterned with openings to form: (i) a first conductivetrace 625 over a first region of the first polymer layer 605, (ii) asecond conductive trace 625 over a second region of the first polymerlayer 605, (iii) a third conductive trace 625 over a third region of thefirst polymer layer 605, and (iv) a fourth conductive trace 625 over afourth region of the first polymer layer 605. In various embodiments,the openings of the resist may have the first pattern, which maintains afirst predetermined distance between each trace of the conductive traces625. The first pattern may include characteristics designed to minimizethe foot print of the flexible printed circuit board 600. Although only,four conductive traces are described with respect to the processesdiscussed above, it should be understood that any number of individualconductive traces can be deposited onto the first polymer. For example,each of the four conductive traces described above could actuallycomprise four separate conductive traces to provide a total of sixteenconductive traces that are individually connected with contact padsdescribed herein (see, e.g., step 6J).

In various embodiments, the conductive traces 625 may be depositedthrough electroplating (e.g., through Cu electroplating, Auelectroplating, Sn electroplating, Ag electroplating, Au/Crelectroplating, etc.) and may be positioned over at least a portion ofthe first polymer layer 605 (e.g., the first region, the second region,the third region, and the fourth region). The electroplating maybeperformed at a current density of about 4.0 mA/cm2 to about 4.5 mA/cm2.In some embodiments, the exposed area or portion of the first polymerlayer 605 may encompass about 2 cm² to about 8 cm². The current may beabout 14 mA to about 18 mA and the duration may be from about 110minutes to about 135 minutes to form the conductive traces 625 having athickness of about 8 μm to about 10 μm. In other embodiments, theexposed area or portion of the first polymer layer 605 may encompassabout 1 cm² to about 12 cm². The current may be about 18 mA to about 28mA and the duration may be from about 35 minutes to about 50 minutes toform the wiring layer 625 having a thickness of about 2 μm to about 5μm.

Following the deposition of the conductive traces 625, the intermediatestructure may be subjected to a strip resist to remove the resistpattern and expose portions of the seed layer (portions without wireformation), and optionally the adhesion layer. The exposed portions ofthe seed layer, and optionally the adhesion layer, may then be subjectedto an etch (e.g., wet etch, dry etch, etc.) to remove those portions,thereby isolating the conductive traces 625 over at least a portion ofthe first polymer layer 605. FIG. 6D shows a top view of the conductivetraces 625 formed in the first pattern on the main body portion 615 ofthe first polymer layer 605.

FIG. 6E shows a subset of conductive traces 630 formed on each of theplurality of end portions 620 in a second pattern. In some embodiments,the subset of conductive traces 630 are formed in manner similardescribed with respect to the conductive traces 625, and thus is notrepeated here. In certain embodiments, the subset of conductive traces630 may be formed in conjunction or simultaneously with the conductivetraces 625. In other embodiments, the subset of conductive traces 630may be formed subsequent to the conductive traces 625. In variousembodiments, the openings of the resist may have the second pattern,which maintains a second predetermined distance between each trace ofthe subset of conductive traces 630. The second pattern electricalconnects each trace of the subset of traces 630 to each trace of theplurality of traces 625, respectively. In some embodiments, firstpattern and the second pattern are the same. In other embodiments, thefirst pattern and the second pattern are different. Likewise, the firstpredetermined distance and the second predetermined distance may be thesame or different. The second pattern may include characteristicsdesigned to minimize the foot print of the flexible printed circuitboard 600 and maximize the number of contacts possible with each branch.FIG. 6F shows a top view of the subset of conductive traces 630 formedon each of the plurality of end portions 620 in a second pattern.

FIG. 6G shows a second polymer layer 635 formed on the first polymerlayer 605, the plurality of conductive traces 625, and each of thesubset of conductive traces 630. The second polymer layer 635 may becomprised of dielectric material (i.e., an insulator). The dielectricmaterial may be selected from the group of electrically flexiblenonconductive materials consisting of organic or inorganic polymers,polyimide-epoxy, epoxy-fiberglass, and the like. In certain embodiments,the dielectric material is a thermoplastic or thermosetting polymer. Forexample, the polymer may be a polyimide, a LCP, silicone, parylene, aPEEK, or combinations thereof. The second polymer layer 635 may becomprised of the same material or a different material from that of thefirst polymer layer 605. For example, the first layer of dielectricmaterial may be a high temperature liquid crystal polymer, and thesecond layer of dielectric material may be a low temperature liquidcrystal polymer.

The forming of the second polymer layer 635 may include depositing andcuring of a polymer material directly on the first polymer layer 605,the plurality of conductive traces 625, and each of the subset ofconductive traces 630. For example, a solution comprised of animidizable polyamic acid compound dissolved in a vaporizable organicsolvent may be applied to the first polymer layer 605, the plurality ofconductive traces 625, and each of the subset of conductive traces 630.The solution may then be heated at a temperature, preferably less than250° C., to imidize the polyamic acid compound to form the desiredpolyimide and vaporize the solvent. The second polymer layer 635 maythen be thinned to a desired thickness by planarization, grinding, wetetch, dry etch, oxidation followed by oxide etch, or any combinationthereof. This process can be repeated to achieve a desired thickness forthe second polymer layer 635. In some embodiments, the second polymerlayer 635 may have a thickness from 1.0 μm to 50.0 μm. In someembodiments, the second polymer layer 635 may have a thickness from 4.0μm to 15.0 μm. In some embodiments, the second polymer layer 635 mayhave a thickness from 5.0 μm to 7.0 μm. FIG. 6H shows a top view of thesecond polymer layer 635 formed on the first polymer layer 605, theplurality of conductive traces 625, and each of the subset of conductivetraces 630.

In various embodiments, the flexible printed circuit board 600 mayfurther comprise one or more contact vias 640 and one or more bond pads645 that support electrical connection with the electronics module ofthe neurostimulator. FIG. 6I shows forming at least one contact via 645on the second polymer layer 635 formed in FIG. 6G that is electricallyconnected to at least one trace of the plurality of conductive traces625 and at least one trace of the subset of conductive traces 630. Insome embodiments, forming the flexible printed circuit board 600 furthercomprises forming at least one contact via 640 in the second polymerlayer 635 of each of the plurality of end portions 620 such that the atleast one contact via 645 is in electrical contact with at least onetrace of the plurality of conductive traces 625 and at least one traceof the subset of conductive traces 630. The contact vias 645 can e.g. beformed with conductive material using conventional lithographic,etching, and cleaning processes, known to those of skill in the art. Thecontact vias 645 may be connected to the at least one trace of thesubset of conductive traces 630 directly or indirectly by way of awiring layer (e.g., a wiring layer formed in conjunction with depositionof the subset of conductive traces 630 in step 6C). In some embodiments,the conductive material is lined on at least a portion of the walls ofthe via hole. In other embodiments, the conductive material fills thevia hole.

FIG. 6J shows forming at least one bond pad 645 on the second polymerlayer 635 of each of the plurality of end portions 620 such that eachbond pad 645 is in electrical contact with at least one contact via 640.In some embodiments, forming the bond bad 645 comprises forming a wiringlayer 650 in a pattern on the second polymer layer 635. The wiring layer650 may be formed in manner similar described with respect to theconductive traces 625 and the subset of conductive traces 630, and thusis not repeated here. FIG. 6K shows a top view of the bonds pads 645formed on each of the plurality of end portions 620.

FIG. 6L shows an optional third polymer layer 655 formed over the secondpolymer layer 635 in a region 660 between the main body portion 615 andthe plurality of end portions 620 in order to reinforce joints betweeneach of the end portions 620 and the main body portion 615. The thirdpolymer layer 655 may be comprised of dielectric material (i.e., aninsulator). The dielectric material may be selected from the group ofelectrically flexible nonconductive materials consisting of organic orinorganic polymers, polyimide-epoxy, epoxy-fiberglass, and the like. Incertain embodiments, the dielectric material is a thermoplastic orthermosetting polymer. For example, the polymer may be a polyimide, aLCP, silicone, parylene, a PEEK, or combinations thereof. The thirdpolymer layer 655 may be comprised of the same material or a differentmaterial from that of the first polymer layer 605 and/or the secondpolymer layer 635.

FIG. 6M shows a final monolithic structure of the flexible printedcircuit board 600 including a main body portion 615 and a plurality ofend portions 620. For example, the flexible printed circuit board 600may be cut from the first polymer layer 605 and the second polymer layer635, and comprises a main body portion 615 and a plurality of endportions 620 extending from the main body portion 605. In someembodiments, the cutting is accomplished using a laser and knowntechniques. Optionally, the flexible printed circuit board 600 may bedetached from the substrate 610.

FIGS. 7A-7H show structures and respective processing steps forfabricating a thin-film branched connector 700 (e.g., a branchedconnector fabricated by injecting and curing a thermosetting polymer) inaccordance with various aspects of the invention. FIG. 7A shows abeginning structure 705 for a branched connector including a main bodyportion 710 and a plurality of end portions 715 extending from the mainbody portion 710. The beginning structure 705 may be formed inaccordance with the processes describe herein with reference to FIGS.6A-6M. For example, the beginning structure 705 may be laser cut in abranched design from first and second polymer layers fabricated withelectroplated traces and bond pads.

FIG. 7B shows each of the end portions 715 at least partially wrappedaround a mandrel 720, respectively, such that each of the end portions715 is in a shape of a cylindrical tube to form an intermediatestructure 725. In various embodiments, the mandrels 720 are selected andthe wrapping is controlled such that the cylindrical tubes comprise oneor more characteristics including a radius, a split or gap, ornon-overlapping ends. The radius is dictated by the outer diameter ofthe mandrels 720 and may be from 300 μm to 900 μm, from 500 μm to 800μm, or from 6000 μm to 700 μm, for example, about 650 μm. In someembodiments, each of the end portions 715 is partially wrapped around amandrel 720, respectively, such that the plurality of cylindrical endportions are a plurality of split cylindrical end portions, and eachsplit cylindrical end portion of the plurality of split cylindrical endportions comprises a gap for the split having a predefined width. Insome embodiments, the mandrels 725 comprise a coating such aspolytetrafluoroethylene (PTFE) for easier removal of the end portions715 from the mandrels 725.

FIG. 7C shows the end portions 715 of the intermediate structure 725being inserted into heat shrink tubes 730, respectively, to form anintermediate structure 735. In various embodiments, the heat shrinktubes 730 are comprised of one or more polymer resins, for example, afluoropolymer such as the FluoroPEELZ® peelable heat shrink tubes,fluorinated ethylene propylene (FEP), etc. FIG. 7D shows intermediatestructure 735 being heated to heat shrink the tubes 730 to define anouter diameter of the cylindrical tubes of the intermediate structure735. The heating process may include baking the structure in an oven,use of a heat gun, application of hot air, like methods, or anycombination thereof. In various embodiments, the intermediate structure735 is heated at 170° C. to 210° C., for example about 190° C., for 15to 40 minutes, for example 25 minutes. Thereafter, the intermediatestructure 735 is cooled (e.g., at ambient temperature), and the mandrels725 are withdrawn to obtain the intermediate structure 740, as shown inFIG. 7E. In various embodiments, the heating process results in each ofthe end portions 715 being in a shape of a cylindrical tube with a lumen745.

FIG. 7F shows a polymer 750 being injected into each of the end portions715 of the intermediate structure 740. In various embodiments, thepolymer is comprised of a medical grade polymer material, for example, apolymer such as epoxy, a polyurethane, a copolymer thereof, or a blendthereof. In some embodiments, the polymer is a thermosetting polymer. Incertain embodiments, the polymer is comprised of a medical grade polymermaterial with a Shore durometer measured on a Shore 00 Scale of greaterthan 70D when cured. (Shore durometer is defined as a material'sresistance to indentation). The polymer 750 may be injected into each ofthe end portions 715 one or more times in order to completely fill thelength of the cylindrical tubes or a portion of the length of thecylindrical tubes to obtain the intermediate structure 755.

FIG. 7G shows intermediate structure 755 being heated to thermally cure(e.g., thermoset) the polymer 750. The heating process may includeheating the structure in an oven, use of a heat gun, application of hotair, like methods, or any combination thereof. In various embodiments,the intermediate structure 755 is heated at 80° C. to 115° C., forexample about 100° C., for 5 to 20 minutes, for example 10 minutes.Thereafter, the intermediate structure 755 is cooled (e.g., at ambienttemperature) and the heat shrink tubes 730 are peeled away to obtain thefinal structure of the thin-film branched connector 700 shown in FIG.7H. The final structure comprises each of the end portions 715 havingthe first and second polymer layers at least partially wrapped around acore made of the polymer 750. In some embodiments, the injection andheating processes result in at least a portion of each of the endportions 715 embedding into the polymer 750, respectively. In someembodiments, the injection and heating processes embeds a portion ofeach of the end portions 715 into the polymer 750, respectively, formingconjoined solid tubes without a lumen.

FIGS. 8A-8E show structures and respective processing steps forfabricating an alternative thin-film branched connector 800 (e.g., abranched connector fabricated by reflowing a predefined thermoplasticpolymer core) in accordance with various aspects of the invention. FIG.8A shows a beginning structure 805 for a branched connector including amain body portion 810 and a plurality of end portions 815 extending fromthe main body portion 810. The beginning structure 805 may be formed inaccordance with the processes describe herein with reference to FIGS.6A-6M. For example, the beginning structure 805 may be laser cut in abranched design from first and second polymer layers fabricated withelectroplated traces and bond pads.

FIG. 8B shows each of the end portions 815 at least partially wrappedaround a polymer tube 820, respectively, such that each of the endportions 815 is in a shape of a cylindrical tube to form an intermediatestructure 825. In various embodiments, the polymer tubes 820 areselected and the wrapping is controlled such that the cylindrical tubescomprise one or more characteristics including a radius, a split or gap,or non-overlapping ends. The radius is dictated by the outer diameter ofthe polymer tubes 820 and may be from 50 μm to 700 μm, from 100 μm to600 μm, or from 100 μm to 450 μm, for example, about 350 μm. In someembodiments, each of the end portions 815 is partially wrapped around apolymer tube 820, respectively, such that the plurality of cylindricalend portions are a plurality of split cylindrical end portions, and eachsplit cylindrical end portion of the plurality of split cylindrical endportions comprises a gap for the split having a predefined width. Insome embodiments, the polymer tubes 820 comprise a thermoplasticpolymer. In certain embodiments, the thermoplastic polymer ispolyurethane.

FIG. 8C shows the end portions 815 of the intermediate structure 825being inserted into heat shrink tubes 830, respectively, to form anintermediate structure 835. In various embodiments, the heat shrinktubes 830 are comprised of one or more polymer resins, for example, afluoropolymer such as the FluoroPEELZ® peelable heat shrink tubes,fluorinated ethylene propylene (FEP), etc. FIG. 8D shows intermediatestructure 835 being heated to heat shrink the tubes 830 to define anouter diameter of the cylindrical tubes of the intermediate structure835, and at the same time melt and reflow the polymer tubes 820 to embedeach of the end portions 815 in the polymer tubes 820, respectively. Theheating process may include baking the structure in an oven, use of aheat gun, application of hot air, like methods, or any combinationthereof. In various embodiments, the intermediate structure 835 isheated at 170° C. to 210° C., for example about 190° C., for 15 to 40minutes, for example 25 minutes. Thereafter, the intermediate structure835 is cooled (e.g., at ambient temperature), the heat shrink tubes 830are peeled away to obtain the final structure of the thin-film branchedconnector 800 shown in FIG. 8E. The final structure comprises each ofthe end portions 815 having the first and second polymer layers at leastpartially wrapped around a core made of the polymer tube 820. In someembodiments, the heating processes result in at least a portion of eachof the end portions 815 embedding into the polymer tubes 820,respectively. In some embodiments, the heating processes embed a portionof each of the end portions 815 into the polymer tubes 820,respectively, forming conjoined solid tubes without a lumen.

While the manufacturing processes of branched connectors have beendescribed at some length and with some particularity with respect to aspecific steps, it is not intended that the processes be limited to anysuch particular set of steps. Instead, it should be understood themanufacturing processes described herein are exemplary embodiments, andthat the manufacturing processes are to be construed with the broadestsense to include variations of the steps to meet specific design and/orperformance need described herein, as well as other variations that arewell known to those of skill in the art. For example, the variousintermediate and final structures described may be adjusted or modifiedwith treatments to increase wettability of the thin-film lead assemblyor to seal the ends of the lumens to meet specific design and/orperformance needs. Furthermore, it is to be understood that other stepshave been omitted from the description of the manufacturing processesfor simplicity and clarity. The omitted steps may include obtaining orfabricating the polymer tubes, obtaining or fabricating the heat shrinktubes, waiting predetermined amounts of time for curing orthermosetting, etc.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to theskilled artisan. It should be understood that aspects of the inventionand portions of various embodiments and various features recited aboveand/or in the appended claims may be combined or interchanged either inwhole or in part. In the foregoing descriptions of the variousembodiments, those embodiments which refer to another embodiment may beappropriately combined with other embodiments as will be appreciated bythe skilled artisan. Furthermore, the skilled artisan will appreciatethat the foregoing description is by way of example only, and is notintended to limit the invention.

What is claimed is:
 1. A thin-film lead assembly comprising: a cablecomprising a proximal end, a distal end, a first supporting structurethat extends from the proximal end to the distal end, and a plurality ofconductive traces formed on a portion of the first supporting structure;an electrode assembly formed on the first supporting structure at thedistal end of the cable, wherein the electrode assembly comprises one ormore electrodes in electrical connection with one or more conductivetraces of the plurality of conductive traces; and a branched connectorcomprising: (i) a main body comprising a second supporting structure anda plurality of conductive connector traces, and (ii) a plurality ofplugs extending from the main body, each plug of the plurality of plugscomprises the second supporting structure and a subset of conductiveconnecting traces from the plurality of conductive connecting traces,wherein each trace from the subset of conductive connecting tracesterminates at a bond pad exposed on a surface of the second supportingstructure, and wherein the plurality of conductive connector traces ofthe branched connector are in electrical contact with the plurality ofconductive traces of the cable, respectively.
 2. The thin-film leadassembly of claim 1, wherein the second supporting structure iscomprised of one or more layers of dielectric material, and thedielectric material is polyimide, liquid crystal polymer, parylene,polyether ether ketone, or a combination thereof.
 3. The thin-film leadassembly of claim 1, wherein the plurality of conductive connectortraces are comprised of one or more layers of conductive material, andthe conductive material is platinum (Pt), platinum/iridium (Pt/Ir),titanium (Ti), gold/titanium (Au/Ti), or any alloy thereof.
 4. Thethin-film lead assembly of claim 1, wherein the second supportingstructure of each plug is planar.
 5. The thin-film lead assembly ofclaim 1, wherein the second supporting structure of each plug is acylindrical tube.
 6. The thin-film lead assembly of claim 5, wherein thesecond supporting structure of each of the plugs comprises a first layerof dielectric material and a second layer of dielectric material withthe subset of conductive connecting traces buried between the firstlayer of dielectric material and the second layer of dielectricmaterial.
 7. The thin-film lead assembly of claim 6, wherein each bondpad is a split annular ring positioned around an axis of the cylindricaltube and exposed on the surface of the cylindrical tube.
 8. Thethin-film lead assembly of claim 7, wherein each split annular ring isspaced apart from one another on the surface of the cylindrical tube bya region of the first layer of the dielectric material.
 9. The thin-filmlead assembly of claim 7, wherein the cylindrical tube comprises: (i)the one or more layers of dielectric material, wherein the first layerof dielectric material defines an outer diameter of the cylindrical tubeand the second layer of dielectric material defines an inner diameter ofthe tube; and (ii) a core that at least partially fills an interior ofthe cylindrical tube defined by the inner diameter of the cylindricaltube.
 10. The thin-film lead assembly of claim 9, wherein the one ormore layers of dielectric material are at least partially wrapped aroundthe core.
 11. The thin-film lead assembly of claim 10, wherein the oneor more layers of dielectric material are formed as a split cylindricaltube wrapped around the core, and the split cylindrical tube comprises agap for the split having a predefined width.
 12. The thin-film leadassembly of claim 11, wherein the first layer of dielectric materialcomprises at least one via for each bond pad, and the via comprises aconductive material for electrically connecting each bond pad to atleast one trace of the subset of conductive connecting traces such thateach trace from the subset of conductive connecting traces terminates ata bond pad.
 13. The thin-film lead assembly of claim 12, wherein thefirst layer of dielectric material is a high temperature liquid crystalpolymer, and the second layer of dielectric material is a lowtemperature liquid crystal polymer.
 14. The thin-film lead assembly ofclaim 13, wherein the core is comprised of one or more layers ofmaterial such that the core has a Shore durometer of greater than 70D.15. A neuromodulation system comprising: a neurostimulator comprising anelectronics module; a cable comprising a supporting structure and aplurality of conductive traces formed on a portion of the supportingstructure, wherein the supporting structure is comprised of one or morelayers of dielectric material; an electrode assembly formed on thesupporting structure, wherein the electrode assembly comprises one ormore electrodes in electrical connection with one or more conductivetraces of the plurality of conductive traces; and a branched connectorformed on the supporting structure at the proximal end of the cable,wherein the branched connector comprises: (i) a main body comprising thesupporting structure and the plurality of conductive traces, and (ii) aplurality of plugs extending from the main body, each plug of theplurality of plugs comprises the supporting structure and a subset ofconductive traces from the plurality of conductive traces, wherein thebranched connector electrically connects each subset of conductivetraces from the plurality of conductive traces to the electronicsmodule.
 16. The neuromodulation system of claim 15, wherein each tracefrom the subset of conductive traces terminates at a bond pad exposed ona surface of the supporting structure.
 17. The neuromodulation system ofclaim 15, wherein the supporting structure of each plug is planar. 18.The neuromodulation system of claim 15, wherein the supporting structureof each plug is a cylindrical tube.
 19. The neuromodulation system ofclaim 18, wherein the supporting structure of each of the plugscomprises a first layer of dielectric material and a second layer ofdielectric material with the subset of conductive traces buried betweenthe first layer of dielectric material and the second layer ofdielectric material.
 20. The neuromodulation system of claim 19, whereineach bond pad is a split annular ring positioned around an axis of thecylindrical tube and exposed on the surface of the cylindrical tube.